Anterior approach to the sciatic nerve block: the effects of leg rotation.

In the anterior approach to the sciatic nerve block, the femur often obstructs the passage of the needle toward the sciatic nerve. In this study, by using a human cadaver model, we assessed how internal and external rotation of the leg influences the accessibility of the sciatic nerve with the anterior approach. Ten lower extremities from five adult cadavers were studied. Needles were used to simulate the anterior approach to the sciatic nerve block. The effect of leg rotation on the needle plane required to reach the sciatic nerve was studied with legs in the neutral position and then with internal and external rotation (45 degrees) of the legs. During needle placement in the neutral position, the needle could not be fully advanced to the level of the sciatic nerve because of obstruction by the lesser trochanter in 80% of attempts. Medial redirection of the needle (10 degrees--15 degrees) allowed it to pass the lesser trochanter but brought the tip of the needle too medial to the sciatic nerve. Internal rotation of the leg facilitated passage of all needles inserted at the level of the lesser trochanter. We conclude that internal rotation of the leg may significantly facilitate needle insertion in the anterior approach to sciatic block.

The division of the sciatic nerve in the popliteal fossa: anatomical implications for popliteal nerve blockade.

UNLABELLED: The sciatic nerve (SN) originates from the L4-S3 roots in the form of two nerve trunks: the tibial nerve (TN) and the common peroneal nerve (CPN). The TN and CPN are encompassed by a single epineural sheath and eventually separate (divide) in the popliteal fossa. This division of the SN occurs at a variable level above the knee and may account for frequent failures reported with the popliteal block. We studied the level of division of the SN in the popliteal fossa and its relationship to the common epineural sheath of the SN. The level of division of the SN sheath into TN and CPN above the knee was measured in 28 cadaver leg specimens. The SN was invariably formed of independent trunks (TN and CPN) encompassed in one common epineural sheath. The SN divided at a mean distance of 60.5 +/- 27.0 mm (range 0 to 115 mm) above the popliteal fossa crease. We conclude that the TN and CPN leave the common SN sheath at variable distances from the popliteal crease. This finding and the relationship of the TN and CPN sheaths may have significant implications for popliteal block. IMPLICATIONS: When performing popliteal block, insertion of the needle at 100 mm above the popliteal crease is more likely to result in placement of the needle proximal to the division of the sciatic nerve than placement at 50 or 70 mm, according to the classical teaching.

Specific nerve blocks: an update.

Recently there has been a considerable increase in interest in regional anesthesia and neural blockade. Many traditional nerve block techniques have been significantly modified to better fit the realm of both inpatient and outpatient surgery. The introduction of long acting local anesthetics with better safety profile as well as better equipment for continuous neuronal blockade has further increased the utility of peripheral nerve blocks. A significant effort has also been invested in studying and improving the safety of various techniques. These developments, coupled with an increased emphasis on teaching of regional blocks by organized anesthesia societies are likely to result in a wider use of these techniques in years to come.

The interaction of temperature with thiopental and etomidate on extracellular dopamine and glutamate levels in Wistar-Kyoto rats subjected to forebrain ischemia.

BACKGROUND: Many studies demonstrate an association between brain damage and the extracellular release of catecholamines and amino acids during cerebral ischemia. While the clinical value of hypothermia during periods of compromised cerebral blood flow and oxygen delivery is well established, the role of anesthetic agents is less clear. Furthermore, the interaction between these agents and hypothermia remains to be elucidated. The purpose of this study was to examine the interactive effects of temperature, sodium thiopental (STP) and etomidate (ETOM) on extracellular neurotransmitter accumulation in the rat corpus striatum during cerebral ischemia. METHODS: Animals were randomly assigned to one of six subgroups: normal saline (NS-norm, pericranial t approximately equal to 37 degrees C, and NS-hypo, t=30 degrees C), etomidate (ETOM-norm and ETOM-hypo), and sodium thiopental (STP-norm and STP-hypo). Microdialysis probes were inserted into the corpus striatum. Dopamine (DA), glutamate, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) levels were measured. At zero minutes, animals received a 10-min infusion of STP (3 mg x kg(-1) x min(-1)), ETOM (0.6 mg x kg(-1) x min(-1)), or NS. Prior to ischemia, animals were given either intravenous STP (10 mg x kg(-1)), ETOM (3 mg x kg(-1)), or NS in bolus form. Each animal was then subjected to 10 min of forebrain ischemia (Is1) followed by a reperfusion interval (Rep1). The entire sequence was then repeated. RESULTS: There were significant interactions between temperature and drug for DA (Is1, P=0.006, Is2, P=0.032) and its metabolites (DOPAC, Is1 P=0.01, HVA, Is1 P=0.03), and for glutamate (Is1, P=0.03, Is2 P=0.06). The nature of this interaction differed for DA and glutamate. The reduction in DA accumulation seen during hypothermia was offset by the addition of either STP or ETOM, whereas the addition of these drugs did not affect the reduced glutamate levels seen with hypothermia. During normothermia, STP and ETOM resulted in diminished DA accumulation compared to controls, yet they increased the accumulation of extracellular glutamate. CONCLUSIONS: Consistent with other studies, hypothermia was associated with diminished extracellular DA concentrations during forebrain ischemia. However, depending on the temperature condition, the addition of STP or ETOM in our forebrain ischemia model led to unexpected findings. The administration of these agents during normothermia diminished ischemia-induced DA accumulation yet resulted in significantly higher concentrations of extracellular glutamate. In contrast, STP and ETOM during hypothermia were noted to significantly offset the DA-reducing effects of hypothermia.

Anatomical landmarks for femoral nerve block: a comparison of four needle insertion sites.

UNLABELLED: The site for needle insertion in femoral nerve block varies significantly among various descriptions of the technique. To determine the site with the highest likelihood of needle-femoral nerve contact, femoral nerve block was simulated in a human cadaver model (17 femoral triangles from 9 adult cadavers). Four 20-gauge 50-mm-long styletted catheters were inserted at four frequently suggested insertion sites for femoral nerve block. At the levels of inguinal ligament and the inguinal crease, the catheters were inserted adjacent to the lateral border of the femoral artery and 2 cm lateral to the femoral artery. During anatomical dissection, we studied the number of catheter-nerve contacts for each of the four insertion sites, and relationships between the femoral nerve and other anatomical structures of relevance to femoral nerve block. Insertion of the needle at the level of the inguinal crease, next to the lateral border of the femoral artery resulted in the highest frequency of needle-femoral nerve contacts (71%). Of note, the femoral nerve was significantly wider (14.0 vs 9.8 mm) and closer to the fascia lata (6.8 vs 26.4 mm) at the inguinal crease than at the inguinal ligament level. We conclude that needle insertion at the inguinal crease level immediately adjacent to the femoral artery produced the highest rate of needle-femoral nerve contacts. The main factors influencing this result include the greater width of the femoral nerve and the more predictable femoral artery-femoral nerve relationship at the inguinal crease level, compared with the inguinal ligament level. IMPLICATIONS: Insertion of a needle at the inguinal crease level and immediately adjacent to the lateral border of the femoral artery results in a high rate of needle-femoral nerve contact.

The practice of peripheral nerve blocks in the United States: a national survey [p2e comments].

BACKGROUND AND OBJECTIVES: A nationwide survey was conducted in order to describe practice patterns surrounding the use of peripheral nerve blocks (PNBs). METHODS: Questionnaires were mailed to 805 anesthesiologists selected systematically from the 1995 ASA and ASRA membership directories. Responses from 409 attending anesthesiologists (response rate 56.5%) were analyzed. RESULTS: While almost all respondents (97.8%) regularly use at least some regional anesthesia techniques in their practices, significantly fewer use PNBs, with most anesthesiologists (59.7%) performing less than five PNBs monthly. Peripheral nerve blocks of the lower extremity (femoral 32 %, sciatic 22 %, popliteal 11%) were less frequently used than PNB of the upper extremity (axillary 88%, interscalene 61%) (McNemar chi-square test = 215.2; P < .001). Anesthesiologists who rated their training in PNBs as adequate (50.8%) devoted a larger percentage of their practice to PNBs than anesthesiologists who rated their training as inadequate (P = .02). Despite the infrequent use of PNBs, 176 respondents (42.6%) predicted that their use of PNBs would increase in the future. CONCLUSIONS: Although this survey indicates that regional anesthesia is frequently practiced in the United States, PNBs and particularly PNBs of the lower extremities remain underutilized.

A comparison of the posterior versus lateral approaches to the block of the sciatic nerve in the popliteal fossa.

BACKGROUND: The main disadvantage of the posterior approach to the block of the sciatic nerve in the popliteal fossa (popliteal block [PB]) is the need to place the patient in the prone position. In this study, the authors examined the clinical utility of a recently described lateral approach to PB that is performed with the patient in the supine position, and they compared its ability to provide reliable surgical anesthesia with that of the posterior approach. METHODS: Fifty patients undergoing surgery of a lower extremity were randomized to receive the PB using either the lateral (n=25) or the posterior approach (n=25). With both techniques, 40 ml 1.5% alkalinized mepivacaine with 1:200,000 epinephrine were injected on successful nerve localization using low current output nerve stimulation. RESULTS: There were no differences in American Society of Anesthesiologists physical status or demographic data between the groups (ASA status, I-III; mean age, 50+/-15 yr; 27 men, 23 women). All patients had good intraoperative analgesia, except one in the lateral group, who reported pain outside the distribution of the sciatic nerve. CONCLUSIONS: Although blockade using the lateral approach took longer to accomplish, both techniques resulted in clinically acceptable anesthesia in the distribution of the sciatic nerve.

Femoral and genitofemoral nerve blocks versus spinal anesthesia for outpatients undergoing long saphenous vein stripping surgery.

Long saphenous vein stripping (LSVS) surgery is often used to treat varicose veins. We tested the hypothesis that femoral nerve block (FNB) with genitofemoral nerve infiltration provides sufficient analgesia and superior recovery characteristics to spinal anesthesia for LSVS procedures in the ambulatory setting. Thirty-six patients were randomized to receive FNB with 30 mL of 3% alkalinized chloroprocaine, and 32 patients received spinal anesthesia with 65 mg of 5% hyperbaric lidocaine. Data collected included patient demographics, time required for induction of and recovery from anesthesia, postoperative anesthesia complications, and patient report of pain severity after the operation. During a follow-up call, a blinded observer noted the onset of any complications, the requirement for analgesics, and the patients' satisfaction with the anesthetic technique. Patients in the FNB group had significantly faster recovery (P < 0.01) and lower incidences of pain (P < 0.05) and complications (P < 0.05) than the patients in the spinal group. All patients who received FNB indicated that they would choose this type of anesthesia in the future, whereas five (15%) patients in the spinal group would refuse spinal anesthesia in the future (P < 0.01). We conclude that FNB is an excellent anesthetic choice for LSVS.

A common epineural sheath for the nerves in the popliteal fossa and its possible implications for sciatic nerve block.

Sciatic nerve block in the popliteal fossa is associated with a highly variable success rate. Frequently, anesthesia is profound in the distribution of both the tibial (TN) and common peroneal nerves (CPN), although the response to nerve stimulation or paresthesia is obtained in the distribution of one division of the nerve. However, anesthesia in the distribution of only one division of the nerve is also a common occurrence under apparently identical clinical circumstances. Looking for a possible role of a common epineural sheath in these phenomena, we injected dye into the epineural sheath of the tibial nerve in 10 cadaver legs and observed its spread within the sheath. Injections of 15 mL and 30 mL of the dye resulted in a proximal spread of 147 +/- 34 mm and 172 +/- 50 mm, respectively, from the injection point 10 cm below the popliteal fossa crease. In a majority of the legs, the dye reached the division of the sciatic nerve in the popliteal fossa, bathing both the TN and CPN. Gross inspection and histologic examination of the sciatic nerve specimens revealed a common epineural sheath enveloping the TN and CPN. The presence of the common epineural sheath and its characteristics may have important clinical implications for sciatic nerve blockade in the popliteal fossa.

The "three-in-one block" for treatment of pain in a patient with acute herpes zoster infection.

BACKGROUND AND OBJECTIVES: Herpes zoster infection in elderly patients frequently results in disabling pain, carries a high risk of postherpetic neuralgia (PHN), and can pose a significant therapeutic challenge. METHODS: We describe a successful use of the perivascular technique of lumbar plexus blockade ("three-in-one block") for treatment of pain during acute herpes zoster infection in an 82-year-old severely ill patient in whom other modalities were contraindicated. RESULTS: Three-in-one block using 40 mL of 0.25% bupivacaine with 1:300,000 epinephrine resulted in excellent pain relief that lasted for 2 weeks. CONCLUSIONS: The perivascular technique of lumbar plexus blockade may be a useful alternative to epidural and paravertebral techniques of lumbar blockade in the occasional patient for whom these other approaches are contraindicated.

Combined popliteal and posterior cutaneous nerve of the thigh blocks for short saphenous vein stripping in outpatients: an alternative to spinal anesthesia.

STUDY OBJECTIVE: To compare a combination of peripheral nerve blocks with spinal anesthesia in ambulatory patients undergoing short saphenous vein stripping. DESIGN: Prospective, randomized study. SETTING: University hospital. PATIENTS: 28 ASA physical status l and II ambulatory surgery patients undergoing short saphenous vein stripping. INTERVENTIONS: 14 patients received a popliteal block (sciatic nerve block at the popliteal fossa) using 30 ml of alkalinized 3% chloroprocaine and a posterior cutaneous nerve of the thigh block with 10 ml of 1% lidocaine. The 14 patients who were randomized to the spinal anesthesia group received 65 mg of 5% hyperbaric lidocaine. MEASUREMENTS AND MAIN RESULTS: There were no significant differences in age and gender between the two groups (mean age 53 +/- 13 years, 8 men and 20 women). Patients in the peripheral nerve block group recovered significantly faster in phase 1 of the postanesthesia care unit (PACU) (67 +/- 10 min vs. 122 +/- 50 min, p < 0.01) and were discharged home sooner (222 +/- 53 min vs. 294 +/- 69 min, p < 0.01) than the patients in the spinal anesthesia group. CONCLUSIONS: The combination of popliteal and posterior cutaneous nerve of the thigh blocks provided adequate anesthesia and a faster recovery profile with a similar subjective acceptance of both anesthetic techniques in ambulatory patients undergoing short saphenous vein stripping in the prone position.

Anatomic considerations for sciatic nerve block in the popliteal fossa through the lateral approach.

BACKGROUND AND OBJECTIVES: The disadvantage of the classic posterior approach to block of the sciatic nerve at the knee level (popliteal nerve block [PNB]) is the need to position a patient in the prone position for performance of the block. In this study on cadavers, a lateral approach to the popliteal nerve in the supine position was investigated, and some anatomic considerations of relevance to popliteal nerve block were addressed. METHODS: In 19 cadaver right legs, the lateral approach to PNB was simulated with a needle, introduced in the groove between the biceps femoris and vastus lateralis muscles 7 cm above the knee, at either 30 degrees or 60 degrees relative to the horizontal plane, and 1 mL of dye solution was injected through the needle. After dissection of the popliteal fossa, the position of the solidified bolus of dye in relation to the popliteal nerve was determined. Additionally, the dye was injected into the popliteal nerve sheath, and the spread of the dye and continuity of the sheaths were determined. RESULTS: In 10 legs, the lateral approach was attempted at a 30 degrees angle and in 9 legs at a 60 degrees angle. The solidified injectates at 30 degrees were closely distributed anterolaterally to the nerve, while injectates at 60 degrees tended to be further from the nerve and scattered along its posterolateral aspect (P = .02). The dye injected into the nerve sheaths traveled 5 to 10 cm within the sheath, surrounding both main divisions of the popliteal nerve, the tibial and the common peroneal nerve. CONCLUSION: A lateral approach to the popliteal nerve with insertion of the needle at a 30 degrees angle relative to the horizontal plane results in predictable approximation of the needle tip to the popliteal nerve. The results also suggest the existence of a continuous neural sheath encompassing the popliteal nerve and its main branches. This may have clinical implications similar to those in perivascular neuronal block.

Supine approach to the sciatic nerve in the popliteal fossa.

PURPOSE: Sciatic nerve block in the popliteal fossa (popliteal nerve block, PNB) is an anaesthetic technique well-suited for operations below the knee. However, difficulty with positioning the patient in the prone position often precludes the classical, posterior approach to the block. In this report, an alternative approach to PNB that can easily be performed with a patient in the supine position is described. CLINICAL FEATURES: Three patients in whom the clinical circumstances precluded the use of the classical approach to PNB are described. In each case, PNB was performed using the alternative, supine approach. With a patient in the supine position, the leg is flexed at both the hip and knee, and supported by an assistant. After the anatomical landmarks of the popliteal fossa are identified, an insulated needle attached to a peripheral nerve stimulator is inserted 7 cm above the popliteal crease, 1 cm laterally to the midline and directed 45 degrees cephalad. Upon obtaining either dorsal or plantar flexion of the foot at the output current of 0.5 mAmp or less. 30-40 ml of local anaesthetic solution are injected. CONCLUSION: The supine approach to PNB allows the use of the block in patients that cannot be positioned in the prone position. Flexion of the leg at the knee greatly facilitates identification of the anatomical landmarks. When combined with a block of the femoral or saphenous nerve, this technique provides excellent anaesthesia for patients undergoing foot and ankle surgery.